This invention relates to an improved process for the chlorination of chlorinated methanes. More particularly, the process of this invention provides for reacting chlorinated methanes and chlorine in a liquid phase environment and in such relative amounts to yield a highly selective product distribution.
The gas phase reaction of chlorine and methyl chloride, methylene chloride and chloroform, is well known in the prior art. The reaction occurs at elevated temperatures i.e., 400.degree. C.-600.degree. C., and at about atmospheric pressure. While gas phase chlorination has been widely used it has several serious drawbacks, some of which are directly related to the required process conditions.
Due to the high temperatures required, side reactions are probable. The most troublesome of the side reactions are those which produce both saturated and unsaturated carbon to carbon bonding. Unsaturated carbon to carbon bonding produces chlorocarbons, such as, vinylidene chloride, tran-- and cis--dichloroethylene and trichloroethylene. These unsaturated compounds contaminate the product thereby requiring additional equipment and energy consumption to effect their removal from the product. The high process temperatures can also result in the production of tar and carbon which cause equipment fouling.
Further, with the gas phase reaction, unreacted methyl chloride must be separated and recycled back to the reactor. This recycle requires a compressor and such compressors are not only expensive but are generally troublesome to keep in service.
Even further, the gas phase reaction does not yield highly selective product distribution when the production of methylene chloride is desired. For example, the typical gas phase reaction produces a methylene chloride to chloroform weight ratio of from about 3 to about 25 depending upon the amount of chlorine fed.
In Japanese Patent Application, Kokai Patent No. 55043002 (published Mar. 26, 1980) it is reported that the liquid phase reaction of chlorine and chlorinated methane obviates some of the drawbacks which are characteristic of the above discussed gas phase reaction. The reported liquid phase reaction is run at low temperature, i.e. 60.degree. C. to about 150.degree. C., and at pressure from about 100 psig to about 430 psig. The low reaction temperature avoids or at least lessens the production of carbon-carbon bonding. The high pressure allows for more economical product separation and eliminates the need for a methyl chloride recycle compressor.
Despite these benefits for this reported liquid phase reaction it is not shown to provide highly selective product distribution when used to produce methylene chloride even though its product distribution is slightly better than that which is obtainable with the gas phase reaction. For example, the reported liquid phase reaction is shown to provide a methylene chloride to chloroform weight ratio which ranges from about 0.4 to 4 depending on the amount of chlorine fed to the reaction.
It is therefore an object of this invention to provide a liquid phase reaction of chlorine and chlorinated methane which is capable of providing high selectivity in product distribution when methylene chloride is the desired product.